It is well known that heart diseases may result in disorders of the cardiac valves. For example, diseases such as rheumatic fever can cause the shrinking or pulling apart of the valve orifice, while other diseases may result in endocarditis, an inflammation of the endocardium or lining membrane of the heart. The resulting defects in the valves hinder the normal functioning of the atrioventricular orifices and operation of the heart. More specifically, defects such as the narrowing of the valve stenosis and/or the defective closing of the valve, referred to as valvular insufficiency, result in an accumulation of blood in a heart cavity or regurgitation of blood past the valve. If uncorrected, prolonged valvular stenosis or insufficiency may cause damage to the heart muscle, which may eventually necessitate total valve replacement.
These defects may be associated with any of the cardiac valves. For example, if the mitral valve stenosis connecting the left auricle with the left ventricle narrows, blood will accumulate in the left auricle. Similarly, in the case of mitral insufficiency, the mitral valve does not close perfectly, and blood in the left ventricle is regurgitated past the closed mitral valve into the left auricle when the ventricle closes.
In many cases, complete valve replacement is required. Mechanical artificial heart valves for humans are frequently fabricated from titanium, prolitic carbon or tissue, including tissue from cows, pigs or humans. Such valves have been used because of their nonthrombogenic properties. Human blood does not coagulate on contact with such valves. Moreover, they are lightweight, hard and quite strong. Therefore, such valves have become widely accepted and used by many surgeons. Any new prosthetic valve or surgical technique associated therewith should account for this. One popular prosthetic valve includes such a hard body and a knit fabric sewing or suture cuff fixedly attached thereto as by drawstrings made of plastics-type material. The sewing cuff is sutured in place on the patient's tissue, and that tissue grows into the fabric providing a secure seal for the prosthetic valve. As will be discussed below, even though this is a widely accepted valve, there are problems and drawbacks.
A standard implantable mechanical heart valve usually has an annular valve housing or body to provide a passageway for blood. Occulders are mounted in the annular body and open or close the blood flow passageway. Usually there are one or two occulders, but occasionally triple occulder configurations have been proposed. On the outside of the valve body there is usually an external, circumferential surface configured as a groove. The purpose of this groove is to facilitate attachment of the above-discussed suture ring to the valve body.
As above mentioned, replacement of heart valves has become a widely accepted procedure. Currently, as many as eighty thousand heart valve prostheses are implanted in the United States alone. This procedure is very expensive. It requires the talents of a highly skilled surgeon, perfusionist and anesthesiologist as well as the supporting staff and equipment required to keep the patient on a heart/lung bypass machine during the operation. While this procedure currently works very well, operating time is still extensive and the longer the patient is on bypass equipment, the greater the risk to the patient. Furthermore, hand suturing is tedious and time consuming further lengthening the time the patient is on cardiopulmonary bypass and hypothermia. This may increase the chances of tissue damage to the patient.
Therefore, there is a need for a heart valve replacement procedure that reduces the surgical time required for the operation.
Still further, many currently used surgical techniques are invasive and often require breaking of bones. This increases the time and difficulty of the recovery. Therefore, there is a need to develop a prosthetic heart valve and a procedure for implanting same that reduces the invasiveness of this surgery.
As above mentioned, hand suturing of prosthetic heart valves in place is widely accepted. However, this requires the opening of the patient's chest wall to gain access to the aortic valve through a transverse incision in the ascending aorta. The distance from the incision down to the valve is usually two to two and one halve centimeters with an aortic lumen diameter of between seventeen and thirty millimeters. This creates a very long and narrow tube into which the surgeon must place sutures. While this is a tedious procedure in an "open chest" case, it is very challenging to accomplish through any small incision between the ribs or through a thoracic inlet, as would be required in any minimally invasive procedure. Therefore there is a need for a device and method that can secure the valve remotely from outside the chest wall.
A further problem associated with suturing some prostheses is that the valve is bulky and reduces the inside diameter of the valve body. A reduced inside diameter of the valve reduces the flow area of the valve resulting in increased transvalvular pressure gradients resulting in increased work for the heart muscle. A reduced flow area for such a valve may adversely influence blood flow characteristics associated with the valve, thereby adversely influencing the performance of the valve. This is very counter-productive to the clinical needs of the prosthesis. It is very hard to develop a mechanical valve that has the same flow characteristics of a living tissue valve. This is especially so of many existing multi-part prostheses. Even the so-called sutureless valves that have been disclosed in the art may have this problem. Heart valve designs have been directed toward minimizing the back pressure or restriction of forward flow by maximizing the cross-sectional area of the valve within a given outer diameter base. Housing attachment means within the valve base narrows the inside diameter of the valve body thereby creating adverse flow characteristics. Therefore, there is a need for a prosthetic valve which has the flow area thereof maximized. Reduced flow area may also result in rapid blood acceleration with a concomitant risk of red cell hemolysis and activation of sensitive enzyme systems such as the clotting system.
Yet a further problem with some prosthetic heart valves and the implanting procedures associated therewith, is that there are unwanted projections remaining on the implanted valve. This is especially so for valves that are sutured in place. Blood clots tend to form around foreign objects in the body. The body's natural defenses try to seal off any foreign material and make it non-threatening. However, there is a danger that the formed blood clots may dislodge into the patient's blood stream, which may cause a major problem.
The sutures used in many existing techniques to sew a cuff in place are knotted and cut off. This leaves raw edges exposed to the patient's blood stream. These raw edges of the cut off suture and knot provide surfaces for clot formation and provide potential for clots to break off into the bloodstream as they are newly formed. Loose clots in the bloodstream are dangerous for the patient as they have the potential for producing a stroke. Clots forming on sutures may also extend onto the valve and produce malfunctions by trapping the valve open or shut. It is common practice to treat a post-surgical patient with heparin or some other anticoagulant to minimize the production of clots. Therefore, there is a need for a prosthetic valve and surgical implanting process that minimizes the amount of foreign objects that remain exposed to the patient after the valve has been implanted. The exposed surfaces may also become a site of infection. Circulating bacteria may become attached and lead to infection at the valve. These infections are notoriously difficult to treat with antibiotics.
Yet another problem arises because it is difficult to effect a secure fit between the prosthesis and the patient's tissue. If there are gaps between the lumen and the valve, a leak may develop causing blood to bypass the valve. This can cause disastrous problems. Additionally, in many of the prostheses that are disclosed in the prior art as being sutureless, there is no way to ensure close approximation of the aortic lumen to the valve base prior to setting fasteners. This has allowed the lumen to pull away from the base and create the just-mentioned leak-generated problems. This is because anatomy is different from patient to patient. It is impossible to make the entire spectrum of valve bases to accommodate such differences in anatomy as would be required by some of the systems presently in use. Additionally, differences in diameter are not just in diameter of the lumen, but in the irregularities of the annulus where the valve is to be placed. Still further, disease and calcification can make the placement of known valves unmanageable. Whatever the cause of the imperfect fit between the prosthetic valve and the lumen, the variation in opening size and/or shape must be accounted for in placing the prosthesis. A securely anchored and tightly fit prosthesis is necessary for a successful outcome.
Furthermore, an improper fit between the prosthetic device and the lumen may greatly increase the duration of the operation or require corrective surgery to replace an improperly placed prosthesis.
Therefore, there is a need for a prosthesis valve that can be securely fit to a patient's lumen in an expeditious and reliable manner.
While the art contains several teachings which could be applied to one or more of the above-mentioned problems, such as the above-discussed cuffs, these disclosures have several drawbacks which are in addition to those already mentioned. For example, these prosthetic valves generally include a sewing ring or suture cuff that has some sort of stiffener therein. An example of such a stiffener is soft plastic. Plastic, even easily molded plastic, may require the patient's tissue to be severely handled and still have puckering even after great precautions have been taken. In this situation, stiffening elements may be more difficult to handle than fully flexible elements and may adversely affect the patient's tissue. Therefore, any new prosthesis valve should use a fully flexible material to attach that prosthesis to the patient to avoid the problems of unduly stressing the patient's tissue during the placement of the valve.
Dacron, Polyester and Teflon have been a very popular material for sewing cuffs. It is slightly stretchable, allowing it to be dilated. Needles readily pass through it without tearing or snagging the fabric fibers and the Dacron material has exceptional implant qualities with a proven track record of bioacceptance that allows ingrowth of endothelial cells. Due to its wide acceptance, it will be commercially advantageous to incorporate Dacron into any new prosthesis valve.
Therefore, there is a need for a prosthesis heart valve which can be tightly placed in a patient without requiring undue stressing of the patient's tissue.
There is yet additional need for a prosthesis heart valve which can have its size and shape expeditiously adjusted to produce a secure, non-leaking, fit to the particular patient, again without placing undue stress on the patient's tissue.
Still further, it is highly desirable for the surgeon to be able to adjust the orientation of the valve in situ. This will permit the prosthesis to be customized to the particular patient. While many known valves can be moved in place, there is still need for improvement in the ease and accuracy of such a step.
Still further, because the position of the junction between the coronary arteries and the aorta is variable, the choice of the location of the placement of the prosthesis should be as great as possible. The high profile of many of the finished sewing cuffs of the known devices severely limits this choice.
Still further, in many instances, it is advantageous for the surgeon to move the prosthesis into various positions relative to the sewing cuff. This will allow the valve to sit at the same level, above or below a certain level. For example, it might be advantageous to seat the valve cuff to be seated above the annulus to maximize the effective orifice area. It will be advantageous to be able to place the prosthesis in the most superior position without interference with the coronary arteries thereby allowing a larger diameter prosthesis to be placed. A lower profile cuff allows the surgeon to place the prosthesis as high as possible without interfering with the coronary artery junction.
Therefore, there is a need for a prosthetic heart valve that has a low profile finished cuff whereby the surgeon can have a greater choice in the superior/inferior placement of the prosthesis valve.
Current prosthetic valves are inefficient because the sewing cuff occupies part of the area available for flow through the valve. If a very small prosthesis is placed in the annulus, there can be a mismatch between the patient's cardiopulmonary requirements and the flow area of the valve. If a patient demands a high level of flow due to a larger size, a small sized valve may result in a significant transvalvular gradient. That is, the pressure in the left ventricle is considerably higher than the pressure in the aorta. This results in increased work for the left ventricular muscle and may predispose to myocardial failure.
If the surgeon suspects that the prosthesis placed is going to be too small, he may elect to enlarge the aortic root. Presently, this is accomplished by opening the aortic annulus opened perpendicular to the plane of the annulus in continuity to the aortomy. The incision is extended along the anterior leaflet of the mitral valve for a varying length. A patch of tissue or fabric material is then stitched to this incision to enlarge it. The procedure allows the insertion of a larger prosthesis into the newly enlarged annulus. However, there is an increased risk to the patient, principally because of the risk of bleeding from the suture line. This site is virtually inaccessible to repair after the aorta is closed.
Therefore, there is a need for a simpler way to expand the aortic annulus. Dilation is preferred, and thus, there is a further need to be able to expand the aortic annulus by dilation. Still further, in minimally invasive surgery, it is sometimes difficult to gain access to a proper fastening plane with a straight instrument. Therefore, it is desirable to be able to use an articulated or curved shaft for a fastening or stapling instrument. Still further, it is often desirable to be able to manipulate the fastening instrument into the most advantageous orientation with respect to the area being stapled.
Therefore, there is a need for a fastening instrument that can be operated to gain access to a great number of fastening planes.
Still further, it is often desirable to stretch and manipulate an element prior to fastening that element to the patient. This is not always possible in minimally invasive techniques using instruments that are available prior to the instruments disclosed herein. Therefore, there is a need for an instrument that can stretch and shape a flexible element prior to and during fastening of that element to a patient in a minimally invasive procedure.
Still further, tough tissue, calcium deposits and the like make fastening an element to a patient difficult, especially in the context of a minimally invasive technique. Therefore, there is need for an instrument that can force a staple through tough tissue and/or calcium covered tissue in a minimally invasive technique. This should be achieved without bunching or damaging the tissue or the element being stapled.
Often, in minimally invasive surgery, it is difficult to place staples in precisely proper locations. This is especially true if the staples are being placed in a circular pattern. Since the circumference of a circle is often not evenly divisible by the width of a staple the gaps between staples are often difficult to establish with proper accuracy so gaps in the staple coverage or bunching of either tissue or material is avoided.
Therefore, there is a need for a device that can be used in minimally invasive surgery for properly placing staples.
Staple placement can be effected by manually locating the staple delivery assembly or by automatically locating the staple delivery assembly. If a manual location technique is used, it is desirable that the surgeon be given an opportunity to choose between a manufacturer's suggestion and his own assessment of the situation. Therefore there is a need for a stapling device for use in minimally invasive surgery that will allow a surgeon to manually locate staples or to select a suggested location for the staples.
As above discussed, the placement of staples in a minimally invasive situation may be difficult to effect in an even manner. Therefore, there is a need for a means and a method for placing staples in a pattern wherein the spacing of the staples is even and no overlap or unwanted gaps occur even if an aorta or other such organ being stapled is an "off size." bbb
Still further, it is desirable that a staple used in a minimally invasive surgical technique drive through the tissue and the material being attached to the tissue in a manner that is most effective. Thus, no bunching or gaping should occur, even if the tissue is tough. The effort to drive the staple through the tissue should be minimized if possible since the mechanical advantage is not the most effective in many situations.
Therefore, there is a need for a staple that can be used in a minimally invasive surgical technique that can be driven through tough tissue in an effective manner.
Still further, there is a need to close the aortomy after completion of valve replacement surgery. This is now achieved using sutures. However, this is time consuming. Therefore, there is a need for a means and a method for closing the aortomy in an efficient and effective manner.